Insofar as the Applicants are aware, there are presently three types of wavelength-division-multiplexing methods in use today: (1) angular dispersion; (2) optical filters; (3) optical absorbers. Our invention utilizes the first of these methods.
The closest prior art known to the Applicants is contained in the literature articles "An Integrated-Optical Approach to the Fourier Transform" by D. B. Anderson, J. T. Boyd, M. C. Hamilton, and R. R. August in IEEE Journal of Quantum Electronics, Vol. QE-13, No. 4, April 1977, and "Wavelength multiplexing in multimode optical fibers" by W. J. Tomlinson, Applied Optics, Vol. 16, No. 8, August 1977, the latter being a general treatment of the state-of-the-art at the time of publication.
There exist a number of wavelength-division multiplexers which are, however, different from the Applicants' invention. The best of these utilize mirrored diffraction gratings in several configurations to achieve differing angular dispersion according to wavelength. Thus, M. Seki et al. disclosed a "20-Channel Micro-optic Grating Demultiplexer for 1.1-1.6 .mu.m Band Using a Small Focusing Parameter Graded-Index: Rod Lens," Electronics Letters, Vol. 18, No. 6, pp. 257-258 (1982). Their design was produced as a twenty-channel demultiplexer utilizing a preferentially-etched silicon echelette grating butted against a Selfoc rod lens. Watanabe and Nosu reported a "Slab waveguide demultiplexer for multimode optical transmission in the 1.0-1.4 .mu.m wavelength region" in Applied Optics, Vol. 19, No. 21 pp. 3588-3590 (1980), which utilized a ground concave grating mirror attached to the end of a planar waveguide, normal to the plane of the guide. With this system the authors were able to demultiplex ten channels. They claim the advantages of (1) stable, rugged construction, (2) no antireflection coatings, and (3) reduced dimensions. Watanabe et al. reported an "Optical grating multiplexer in the 1.1-1.5 .mu.m wavelength region" in Electronics Letters, Vol. 16, pp. 108-109 (1980), which could multiplex ten channels in the 1.1-1.5 .mu.m wavelength range using a planar diffraction grating mirror made from anisotropically etched silicon. Aoyama and Minowa, in "Optical demultiplexer for a wavelength-division multiplexing system," Applied Optics, Vol. 18, No. 8, pp. 1253-1258 (1979), reported a demultiplexer for five channels in the 0.8-0.9 .mu.m range using a commercially available grating mirror and homogeneous lenses.
None of the foregoing is as effective as the Applicants' invention which, besides, has economies in fabrication and use, and enlarged channel processing capabilities which completely surpass expectations.